from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import logging
import os
import random

from builtins import object

from hdfswrapper import settings
from hdfswrapper.connections import Connection

CONN_ENV_PREFIX = 'GRASSHIVE_CONN_'


class BaseHook(object):
    """
    Abstract base class for hooks, hooks are meant as an interface to
    interact with external systems. HDFS,  HiveHook, return
    object that can handle the connection and interaction to specific
    instances of these systems, and expose consistent methods to interact
    with them.
    """

    def __init__(self, source):
        pass

    @classmethod
    def get_connections(cls, conn_id):
        session = settings.Session()

        db = (session.query(Connection).filter(Connection.conn_id == conn_id).all())
        if not db:
            raise Exception(
                "The conn_id `{0}` isn't defined".format(conn_id))
        session.expunge_all()
        session.close()
        return db

    @classmethod
    def get_connection(cls, conn_id):
        environment_uri = os.environ.get(CONN_ENV_PREFIX + conn_id.upper())
        conn = None
        if environment_uri:
            conn = Connection(conn_id=conn_id, uri=environment_uri)
        else:
            conn = random.choice(cls.get_connections(conn_id))
        if conn.host:
            logging.info("Using connection to: " + conn.host)
        return conn

    @classmethod
    def get_hook(cls, conn_id):
        connection = cls.get_connection(conn_id)
        return connection.get_hook()